Engine control systems inject fuel into the engine to maintain a desired air/fuel ratio necessary for controlling regulated emissions. In certain applications, the amount of fuel injected is based on an estimate of air entering the cylinder to maintain a desired air fuel ratio. The estimate of air entering the cylinder is based on a measurement of airflow entering the intake manifold of the engine. In addition, other parameters such as engine speed are utilized.
Because injecting fuel takes a finite amount of time and, in certain cases, fuel is injected before the air actually enters the cylinder, the actual amount of air that enters the cylinder is different from that which was estimated and used in the calculation of the fuel injection amount. For example, engine operating parameters, such as throttle position, can change between the time when the estimate was made and fuel injection amount calculated and the time when the fuel was actually injected. Thus, an error in the air fuel ratio results.
One method of improving air/fuel ratio control is to predict a future value of air entering the cylinder (or a future value of manifold pressure) and then use this prediction to calculate the fuel injection amount. The prediction is based on the current operating conditions and various models representing the physical processes of the internal combustion systems. Such a system is disclosed in U.S. Pat. No. 5,069,184.
The inventors herein have recognized a disadvantage with the above approach. For example, the approach attempts to predict the future value of air entering the cylinder. Thus, there will always be an error because perfect prediction is not possible. The prediction error will translate directly to an error in the air/fuel ratio, thereby affected the production of regulated emissions.